Catching more air: A method to spatially quantify aerial triazole resistance in Aspergillus fumigatus

Airborne triazole-resistant spores of the human fungal pathogen Aspergillus fumigatus are a significant human health problem as the agricultural use of triazoles has selected for cross-resistance to life-saving clinical triazoles. However, how to measure the health risk posed by these inhaled spores remains unclear. Here, we describe a method for cost-effective wide-scale outdoor air sampling to measure both spore abundance as well as antifungal resistance fractions. We show that prolonged outdoor exposure of sticky seals placed in delta traps, when combined with a two-layered cultivation approach, can consistently yield sufficient colony-forming units (CFUs) for the quantitative assessment of aerial resistance levels at a spatial scale that was up to now unfeasible. When testing our method in a European pilot sampling of 12 regions, we demonstrate that the triazole-resistant fraction of airborne spores is widespread and varies between 0 and 0.1 for itraconazole ([~]4 mg/L) and voriconazole ([~]2 mg/L). This method facilitates the assessment of health risks by pinpointing potential hot- and coldspots of environmental resistance selection. This efficient and accessible air sampling protocol opens up extensive options for fine-spatial sampling and surveillance studies. IMPORTANCEAspergillus fumigatus is an opportunistic fungal pathogen which humans and other animals are primarily exposed to through inhalation. Due to the limited availability of antifungals, resistance to the first choice class of antifungals, the triazoles, in A. fumigatus can make infections by this fungus untreatable and uncurable. Here we describe and validate a method that allows for the quantification of airborne resistance fractions and quick genotyping of A. fumigatus TR-types. Our pilot study provides proof of concept of the suitability of the method for use by citizen scientists for large-scale spatial air sampling. Spatial air sampling opens up extensive options for surveillance, health-risk assessment, and studying the ecology of A. fumigatus and the development of triazole resistance.